10.1021/jo951643d
The study investigates the semi-π analogue of double hyperconjugation, known as "hyperconjugation/conjugation," in 4-isopropylidenecyclohexyl mesylate (4-OMs) and compares it with the saturated analogue, trans-4-isopropylcyclohexyl mesylate (5-OMs). The researchers found that the unsaturated substrate 4-OMs reacts only four times faster than the saturated substrate 5-OMs in 97% trifluoroethanol, indicating no significant through-bond interaction of the double bond with the reactive center. This is attributed to less than ideal overlap of the γ,δ π orbitals with the R, σ orbitals. However, when an electron-rich tin atom is attached to the 4-position, it provides a large rate enhancement and changes the mechanism to carbocation formation through double hyperconjugation. The study concludes that the π bond does not effectively stabilize positive charge through two stages of conjugation in the studied system, suggesting that the hyperconjugation/conjugation mode may not be a viable mechanism under the given conditions.
10.1071/CH16710
The study reports on the successful synthesis and characterization of two 28-membered, 2,2'-bipyridine-containing macrocycles in high yield. The first macrocycle was formed through a Williamson ether synthesis, and upon reduction with sodium borohydride, the second macrocycle was produced quantitatively. These macrocycles, which contain a 2,2'-bipyridine unit, are potentially useful components for creating a variety of interlocked architectures, including catenanes, rotaxanes, and molecular machines. The research builds upon previous work by Sauvage, Stoddart, and Feringa, who were awarded the 2016 Nobel Prize in Chemistry for their contributions to the design and synthesis of molecular machines, and it aims to improve upon the yield-limiting macrocyclisation reactions that have historically been a challenge in the field. The study also discusses the use of high-yielding synthetic strategies and the potential for future investigations into the metal-complexation properties of these ligands and their application in forming interlocked structures.
10.1080/24701556.2021.1917611
The research focuses on the synthesis, crystal structure, and antibacterial activity of three new complexes: two copper(II) complexes, [Cu(L1)2] (1) and [CuL2(N3)] (2), and one cadmium(II) complex, [Cd(L3)2] (3). The ligands L1, L2, and L3 are derived from 3-bromo-5-chlorosalicylaldehyde and different amines, resulting in N,O- or N,N,O-donor monocondensed Schiff bases. The synthesis involved reactions in ethanol, with the addition of NaBH4 and metal salts like Cu(ClO4)2·6H2O and Cd(CH3COO)2·2H2O. Characterization included IR, UV-Vis, and elemental analysis, with crystal structures determined by X-ray crystallography. Antibacterial assays were conducted on Gram-positive (B. subtilis, S. aureus) and Gram-negative (E. coli, P. aeruginosa) bacteria using the MTT method to determine IC50 values. The complexes showed promising antibacterial activities, with complex 1 being particularly effective against S. aureus, surpassing the activity of Penicillin G.
10.1039/c8nj01223g
The research focuses on the green synthesis of gold (Au), silver (Ag), platinum (Pt), and palladium (Pd) nanoparticles using sodium rhodizonate as a bifunctional reducing and stabilizing agent. The study involves the preparation of these nanoparticles in water through a single-step process and evaluates their catalytic efficiency in reducing 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using sodium borohydride (NaBH4) and in the dual-catalytic oxidation of formic acid followed by the reduction of methyl orange (MO). The synthesized nanoparticles were characterized using UV-Vis spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, and zeta potential measurements to determine their size, morphology, crystallinity, elemental composition, and surface charge. The catalytic activities of the nanoparticles were assessed through UV-Vis spectrophotometer monitoring of the absorbance changes at specific wavelengths, corresponding to the reactants and products in the reduction reactions.
10.3987/COM-04-10206
The research focuses on the development of a new synthetic method for producing 2,3,6-tri- and 2,3,5,6-tetrasubstituted pyridine derivatives, which are key structural components of thiostrepton-type macrocyclic antibiotics. The synthesis is achieved starting from L-α-aspartic acid through the use of an α-dehydroamino acid derivative. The study involves a series of chemical reactions, including esterification, reduction, oxidation, and cyclization, utilizing reagents such as DCC, HOBt, NaBH4, SO3.pyridine, Jones reagent, MnO2, MeI, Ag2CO3, and Pd-C/H2. The analyses used to characterize the synthesized compounds include melting point measurements, infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis, which confirm the structure and purity of the products.
10.1016/S0040-4020(00)01008-5
The research focuses on the synthesis of spiroazabicycloalkane amino acid scaffolds, which serve as reverse-turn inducer dipeptide mimics. These conformationally constrained molecules are designed to mimic Ala-Pro dipeptide units or more generally, the central (i+1 and i+2) residues of β-turns in peptide chains. The methodology involves a series of chemical reactions starting from known compounds, utilizing reagents such as LiEt3BH, Ac2O, allyltributyl tin, BF3.Et2O, OsCl3, and NaBH4, among others, to produce the desired scaffolds. The experiments include hydrogenolysis, hydrolysis, protection of nitrogen atoms, dihydroxylation, oxidation, and olefination steps. The analyses used to characterize the intermediates and final products encompass 'H and 13C NMR spectroscopy, elemental analysis, mass spectrometry, and optical rotation measurements. Single crystal diffraction analysis was also performed to secure the configuration of the diastereoisomeric alcohols. The study successfully demonstrates a practical approach to synthesize these constrained scaffolds, which could potentially improve peptide-receptor affinity by interacting with hydrophobic pockets, thereby enhancing the metabolic stability of peptides.
10.1016/j.tet.2016.11.035
The research focuses on the enantiospecific synthesis of functionalized polyols derived from tartaric acid, utilizing Ley's dithiaketalization method. The study demonstrates the application of this strategy in the total synthesis of achaetolide, a decanolactone natural product. The experiments involved the synthesis of chiral tetrols and 1,2,4-triols with varied substitutions, with a key reaction being the Ley’s dithianylation of an alkynyl ketone derived from tartaric acid. The synthesis strategy was executed in several steps, starting from the addition of alkynyl Grignard reagents to tartaric acid amides, followed by stereoselective reduction, and elaboration to polyol systems. The research employed various reactants, including tartaric acid, alkynyl Grignard reagents, 1,3-propanedithiol, and NaBH4, among others. Analytical techniques used throughout the experiments included column chromatography, TLC, NMR spectroscopy, and HRMS for compound characterization and yield determination. The study resulted in the total synthesis of achaetolide in 14 steps from the bis-Weinreb amide of tartaric acid, with an overall yield of 9.5%.
10.1021/ic990773s
The research focuses on the synthesis, spectroscopic characterization, crystal structure, and theoretical calculations of the dinuclear nickel(0) complex [Ni2(μ-CO)(CO)2(μ-dppa)2] (where dppa is bis(diphenylphosphino)amine). The complex was synthesized via two methods, yielding a stable microcrystalline yellow solid. The first method involved the reaction of Ni(CO)4 with the dppa ligand in benzene, while the second method used NiCl2·6H2O with dppa in methanol and sodium tetrahydroborate as a reducing agent with carbon monoxide. The synthesized complex was characterized using elemental analysis, infrared (IR) spectroscopy, proton and phosphorus-31 nuclear magnetic resonance (1H and 31P NMR), and cyclic voltammetry. The crystal structure was determined through X-ray diffraction, revealing a triclinic crystal system with a P1 space group and specific unit cell dimensions. Theoretical calculations using a semiempirical PM3 Hamiltonian were also conducted to predict bond orders and reactivity, supported by the Fukui function analysis. The complex was found to absorb carbon monoxide, leading to the formation of a mixture of nickel carbonyl compounds, and showed electrochemical behavior indicative of successive oxidation of the metal centers.
10.1016/0008-6215(90)80082-E
The research presents a study on the impact of (1-13C)-substitution on the 'H- and 13C-nuclear magnetic resonance (n.m.r.) spectra of symmetric and dissymmetric alditols, which are acyclic carbohydrate derivatives. The purpose of the study was to assess the effect of 13C-substitution on their spectral properties and to evaluate the potential of using these couplings in conformational studies of these compounds. The researchers synthesized (1-13C)alditols by reducing the corresponding (1-13C)aldoses with sodium borohydride (NaBH4). They analyzed the n.m.r. spectra of these compounds and found that 13C-substitution effectively removed magnetic equivalence, creating composite spectra from overlapping '3C-coupled and non-coupled subspectra. This made the spectra of symmetric alditols more complex to interpret but also allowed for the measurement of 13C-1H and 13C-13C spin-coupling constants, which can be valuable for conformational analysis. The study concluded that while the spectra of symmetric alditols are more challenging to interpret due to the 13C-substitution, the couplings obtained can provide insights into the conformational properties of these compounds, although further studies are needed to define the relationships appropriate for particular coupling pathways.
10.1021/ja00212a030
The study presented in the document investigates the biomimetic oxidation of 1,2-diols using molecular oxygen in the presence of iron-porphyrin catalysts, mimicking the function of metal-containing oxidases and oxygenases found in biological systems. The researchers utilized a catalytic system comprising an iron-porphyrin complex, 1-benzyl-3-carbamoyl-1,4-dihydropyridine (BNAH), and molecular oxygen to selectively cleave the carbon-carbon bonds of aryl-substituted ethane-1,2-diols at room temperature, producing aldehydes or ketones as the main oxidation products. The reaction rates were influenced by the steric hindrance of substituents in both the catalysts and diols, and no significant differences in reactivities were observed between the two stereoisomers (meso and dl) of the diols. The study provides insights into the mechanism of the diol cleavage reaction, which involves the initial binding of the diol to the active catalyst forming an intermediate complex, followed by a rate-determining breakdown step in the catalytic cycle. The findings have implications for understanding the activation of molecular oxygen and oxygen atom transfer to organic substrates, processes that are crucial for cytochrome P-450 in biological systems.
10.1016/j.tetlet.2011.07.078
The research focuses on the stereoselective synthesis of the peptide moiety of jamaicamides, which are marine natural products with sodium channel blocking properties. The synthesis begins with natural amino acids, L-alanine and N-Boc-β-alanine, and utilizes Meldrum's acid as a key reactant. The researchers detail the preparation of two segments of the peptide: the pyrrolidone ring and the N-Boc-β-methoxy enone carboxylic acid. Various reagents such as EDC·HCl, DMAP, NaBH4, and LiHMDS are used in a series of reactions including condensation, reduction, and amide bond formation. Analytical techniques likely employed, though not explicitly mentioned in the paragraph, include NMR spectroscopy and mass spectrometry for compound characterization. The study also discusses alternative routes and yields for different steps, aiming to optimize the synthesis process.
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